The present invention relates to an apparatus for filtering and separating flow medium by reverse osmosis, ultrafiltration, and microfiltration. A plurality of essentially laminar or sheet-like filter elements are disposed next to, and spaced from, one another in such a way as to form respective flow chambers for the flow medium. Filtrate that is produced is withdrawn at the end face of at least one hole formed in a filter element and disposed essentially at right angles to the planar surface of that filter element.
With apparatus of this type (German Offenlegungsschrift 35 07 908 A-Hilgendorff dated Sept. 11, 1986 and corresponding British Pat. No. 2,173,421 A-Hilgendorff et al dated Oct. 15, 1986, both belonging to the assignee of the present invention), the filter elements (diaphragms) were up to now accommodated in separate support frames that comprised an outer ring and an inner ring, between which were disposed a lattice and a fabric mesh having projections. Resting against the outer and inner rings, any desired number of such support frames were disposed next to one another while sandwiching therebetween a filter element, with the outer and inner rings assuring a fixed connection of the thus formed apparatus. It has been shown that with the use of such element carriers against those parts of the support frame that contact the filter element, in the previously described example the lattice with the projections disposed thereon, the filtrate yield is reduced during the course of time, resulting in an overall reduction of the separating efficiency of the apparatus.
The reason for this is that in the flow shadows of the contact points of the projections against the filter element surface, crystallization seeds are formed for the precipitation of the materials contained in the flow medium and for increased deposition of impurities. Although the reduction of the separating efficiency of the apparatus can be counteracted by increasing the velocity of the flow medium in the apparatus, so that the formation of crystallization seeds on the contact points and the deposition of dirt thereon is reduced, this method on the one hand is insufficient to continuously maintain a constant separating capacity for the apparatus, and on the other hand the increase of the velocity of the flow medium is accompanied by an increased energy consumption for the pump devices, and the apparatus must be designed for the increased pressure difference, which in turn makes the device considerably more expensive.
It is an object of the present invention to provide an apparatus with which in a straightforward manner the formation of crystallization seconds on the surface of the filter elements, and hence a deposition of impurities carried by the flow medium, is reduced, so that in a straightforward manner the separating capacity of the apparatus is retained, and the apparatus as a whole can be manufactured in a more economical manner than was possible with the heretofore known apparatus.